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Introduction

The focus of this article is the rationale for use of a modality and its safety considerations. Contraindications, precautions, risks, and safety considerations are oulined in detail by Houghton et al. (2010) [1]. Clinical indications, application parameters, and equipement maintenance are not included.

Electrical Stimulation - TENS and IFC

Electrical stimulating currents such as transcutaneous electrical nerve stimulation (TENS) and interferential current (IFC) utilize electrical energy, the flow of electrons or other charged particles from one area to another, causing depolarization of muscle or nervous tissue. Electrical stimulation has most commonly been used for the modulation of pain through stimulation of cutaneous sensory nerves and the following analgesic mechanisms [2]:

activation of large diameter A-beta fibers inhibits the pain transmission, carried by A-delta and C afferent fibers, from the spinal cord to the brain - also known as the gate control theory of pain

stimulation of A-delta and C fibers causes the release of endogenous opioids (endorphin and enkephalin) resulting in prolonged activation of descending analgesic pathways

Tissues with high resistance to electrical current include skin, bone, and necrotic tissue - electrodes should not be placed directly over bony prominences

Factors increasing skin impedance include the presence of hair and oil, and cooler skin temperatres

Applying IFC or TENS in combination with a thermal modality is not recommended as it increases the likelihood of an adverse effect

Large electrodes are more comfortable and allow current to travel deeper but the target is less specific - only large electordes should be used with medium frequencies (IFC) to disperse the current

Placing electrodes farther apart will allow the current to travel deeper - at lease 1 inch apart for pain control

With any electrical device, increasing the intensity will first cause an electrical sensation followed by a motor repose and finally noxious stimuli

Remember that the modulation of pain is not treating the cause of pain

Thermal Energy

Thermotherapy and cryotherapy, the application of therapeutic heat and cold, are referred to as conductive modalities - they utilize the conduction of thermal energy to produce a local and occasionally a generalized heating or cooling of superficial tissues with a maximum depth of penetration of 1 cm or less [2].

Increasing local tissue temperature accelerated the healing process by dilating blood vessels and shifting the oxy-hemoglobin dissociation curve to increase the oxygen and nutrient supply to the tissue [3], as well as stimulating fibroblast proliferation [4], accelerating endothelial cell proliferation [5], and improved phagocytic activity of inflammatory cells [6]. Heat is believed to have a relaxing effect on muscle tone by reducing muscle spindle and gamma efferent firing rates; there is also the theory that relaxation of muscle is assumed to occur with the disappearance of pain [2].

Contraindications

Precautions

Risks

DVT or thrombophlebitis

Hemorrhagic conditions

Reproductive organs

Impaired cognition or communication

Acute injury or inflammation (local)

Impaired circulation or sensation (local)

Damaged or at-risk skin (local)

Infection or tuberculosis (local)

Malignancy (local)

Recently radiated tissue (local)

Skin disease (local)

Active epiphysis

Cardiac insufficiency or failure

Pregnancy

Eyes, anterior neck, carotid sinus

Metal (jewelry, metal implants or staples, bullets)

Topical irritants

Burn

Fainting or dizziness (vaso-vagal response)

Bleeding (open wounds)

Additional Considerations

Test sensory integrity by asking patients to differentiate between hot and cold stimuli

Wrap heating pads in 6 - 8 layers of toweling to protect the skin from burns

If core temperature is not maintained, reflex shivering results in increased tone

Re-warming period should be at least twice as long as the treatment time (too frequent application increases likelihood of frostbite)

Hierarchy of cooling, from most to least efficient, is as follows: ice immersion, crushed ice, frozen peas, gel pack – choose an agent with less cooling potential if the patient has risk factors for an adverse reaction

Ultrasound

Ultrasound utilizes sound energy, pressure waves created by the mechanical vibration of particles through a medium. The flow of ultrasound may be delivered as an uninterrupted stream (continuous mode) or delivered with periodic interruptions (pulsed mode). Ultrasound is classified as a deep heating modality capable of producing a temperature increase in tissues of considerable depth because it travels very well through homogenous tissue (e.g. fat tissue) [11][12]. Traditionally it has been used for its thermal effects but it is capable of enhancing healing at the cellular level. Continuous ultrasound is most commonly used when thermal effects are desired but non-thermal effects will also occur [13]. It has been shown to alter all phases of tissue repair: stimulates phagocytic activity of inflammatory cells such as macrophages [14], and promotes release of chemical mediators from inflammatory cells which attract and activate fibroblasts to the site of injury, stimulates and optimizes collagen production, organization and ultimately functional strength of scar tissue [15]. An examination of research studies to assess changes in blow flow with ultrasound produced inconclusive results; however, recent studies show that nitric oxide released by ultrasound therapy may be a potent stimulator of new blood vessel growth at the site of injury [16]. Ultrasound also aids in pain relief and the literature has proposed reduced conduction of pain transmission as a possible mechnism for the analgesic effects [17]. More recently, low-intensity pulsed ultrasound has been shown to accelerate the rate of healing of fresh fractures due to the enhancement of angiogenic, chondrogenic, and osteogenic activity [18].

Pulsed Ultrasound

Contraindications

Precautions

Risks

Hemorrhagic conditions

Eyes, anterior neck, carotid sinus, reproductive organs

Electronic device

DVT or thrombophlebitis (local)

Malignancy (local)

Pregnancy (local)

Tuberculosis (local)

Recently radiated tissue (local)

Active epiphysis

Acute injury or inflammation

Damaged or at-risk skin

Infection

Skin disease

Impaired circulation or sensation

Impaired cognition or communication

Plastic or cement implants

Regenerating nerves

Pain

Surge

Continuous Ultrasound

Contraindications

Precautions

Risks

Acute injury or inflammation

Hemorrhagic conditions

Impaired circulation or sensation

Impaired cognition or communication

Eyes, anterior neck, carotid sinus, reproductive organs

DVT or thrombophlebitis (local)

Infection or tuberculosis (local)

Malignancy (local)

Recently radiated tissue (local)

Pregnancy (local)

Skin disease (local) e.g. psoriasis, eczema, etc.

Electronic device (local)

Plastic or cement implants (local)

Active epiphysis

Chronic wound

Damaged or at-risk skin

Regenerating nerves

Burn

Pain

Surge

Additional Considerations

Test sensory integrity by asking patients to differentiate between hot and cold stimuli or between light touch and painful stimuli

Avoid pre-treatment of the area with superficial heating or cooling agents - cumulative effect of a hot pack and ultrasound can lead to skin damage

Recommended treatment is 2 – 3x the effective radiating area (ERA)

Circular head movement produces more even delivery of ultrasound energy since hot spots are dissipated better

To minimize the impedance difference at the steel/air interface, a suitable coupling medium must be utilized

LASER

Light Amplification for the Stimulated Emission of Radiation (LASER) utilizes electromagnetic radiant energy, the movement of photons through space. The low-power or cold laser produces little or no thermal effects but seems to have some significant effect on soft-tissue and fracture healing as well as on pain management. Light at the wavelength typically employed in laser therapy is readily absorbed by enzymes, hemoglobin, fibroblasts, and neurologic tissue. Laser has been shown to stimulate cell degranulation causing the release of potent inflammatory mediators such as growth factors [20], activate phagocytic processes at the site of injury [21], and activate fibroblast cell function to increase collagen deposition and improve tensile strength [22]. Some reports also show a small decrease in edema produced by inflammation following laser therapy [23]. Absorption by hemoglobin releases nitirc oxide resulting in endothelial cell proliferation and increased microcirculation [24]. Low dosages also result in significantly decreased sensory nerve conduction velocity effect in reducing pain [25].

Contraindications

Precautions

Risks

Hemorrhagic conditions

Eyes, reproductive organs

DVT or thrombophlebitis (local)

Malignancy (local)

Pregnancy (local)

Tuberculosis (local)

Impaired cognition or communication

Infection

Photosensitivity or systemic lupus

Recently radiate tissue

Anterior neck, carotid sinus

Eye damage

Bleeding (open wounds)

Additional Considerations

Reduce the risk of adverse effect on the eyes by applying laser in a closed environment, providing protective goggles when necessary, and performing an 'in-contact' technique

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